Array.fromAsync polyfill

TC39 is considering a new standard [Array.fromAsync convenience
method][Array.fromAsync]. This is a standalone polyfill for that.

[Array.fromAsync]: https://github.com/tc39/proposal-array-from-async

Requirements

This polyfill requires ES 2018 (which must include [support for async
iterators][]).

[support for async iterators]: https://kangax.github.io/compat-table/es2016plus/#test-Asynchronous_Iterators

Installation

In Node:
``bash
npm install array-from-async
`
…then:
`js
import fromAsync from 'array-from-async';
`

In web browsers or Deno:
`
import fromAsync from '//unpkg.com/array-from-async';
`

Description


This is a standalone implementation of the proposed Array.fromAsync
function. Unlike typical polyfills/shims, it does not mutate the global Array
constructor; instead, it exports an equivalent function.

Similarly to [Array.from][],
fromAsync would be a static method
of the Array built-in class, with one required argument
and two optional arguments: (items, mapfn, thisArg).

But instead of converting an iterable to an array,
it converts an async iterable to a promise
that will resolve to an array.

`js
async function * f () {
for (let i = 0; i < 4; i++)
yield i * 2;
}

// Resolves to [0, 2, 4, 6].
await fromAsync(f());
`

[Array.from`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/from

For more information, see the [Array.fromAsync][] explainer.